Dust generated from particulate materials creates many problems. In industry, dust can be a health hazard due to skin contact, ingestion of the dust by breathing, and/or explosion and fire hazards. Dust can also be a nuisance as when it settles in undesirable locations as a dusty material is dispersed or otherwise handled.
Particles having a size less than about 250 micrometers, i.e., passing through a 60 mesh U.S. Standard Sieve Series screen, are defined as dust. See, Goss et al. "A Technique for Dust Measurement", Pesticide Formulations and Application Systems: Eighth Volume, American Society for Testing and Materials (ASTM), 1989, pp. 98-103, p. 99.
Many attempts have been made to bind the dust in some manner and to control it to some extent. For example, attempts have been made to allay dust by misting water in the air so as to maintain an excess of humidity in the area; however, this particular expedient is not always available, and is undesirable with absorbent solids. Oils have also been used on some materials to alleviate the dust problem. Such methods are inapplicable when it is desired that the material be substantially dry as with sorptive materials because the addition of water or oil also reduces the sorption capability of the material. Moreover, water- or oil-treated dusty materials have a relatively short shelf life.
An alternative method of controlling dust is to pelletize the material by forming a fluid paste by with a binder and then extruding the paste. Typically, the produced pellets are dense and strong. However, pellets are undesirable when a material having a relatively large surface is desired, because pelletizing reduces the surface area of the material. Moreover, pelletizing adds to the cost of the final product.
Polytetrafluoroethylene (PTFE) resins also can be utilized to control dust. See, for example, U.S. Pat. No. 3,993,584 to Owen et al. However, use of PTFE in many situations is undesirable because PTFE is costly, a heating step is required, and the applied PTFE cannot be later dissolved away.
The present invention provides substantially dust-free granules of a normally dusty inorganic solid material by distributing a relatively small amount of a vinyl polymer thereon. Dusting is reduced while maintaining the sorption capabilities of the inorganic solid material. Moreover, the present granules have a much better shelf life than similar granules treated with oil or water for purposes of dust abatement. The shortcomings of the aforementioned prior art dust abatement methods and compositions are thereby overcome, or at least minimized.